Q: I redeemed a gift  card a while back and now I don't have the balance for it and when I try to redeem it I can't Because I already redeemed it. PLEASE HELP

A gift card can only be redeemed once, there is no need to try and redeem it again.

To see what, if any, balance you have remaining on the account that you redeemed it onto : See your iTunes credit balance - Apple Support

To see what you've bought on the account, and therefore potentially used some/all of it : See your purchase history in the iTunes Store on a Mac or PC - Apple Support

What do you mean you redeemed it and you don't have the balance for it. If you redeemed the card to your iTunes account, the balance would show there. Check your purchases to ensure that you did not spend that amount already, or that you didn't have an outstanding debt in your iTunes account that needed to be settled.

If you have a question about your iTunes account, then you can contact iTunes support. https://www.apple.com/emea/support/itunes/contact.html

This is a user to user support forum. You are not addressing Apple here, so no one here would know what happened to your account. If you wish to know where the amount went, then you need to contact Apple. Only they can answer that question. You were given a links to check your account balance, and a link to contact iTunes support.